1. Field of the Invention
This invention is in the field of optical instrumentation and more particularly relates to apparatus for indicating and measuring an asphericity of the exterior surface of an eye.
2. Description of the Prior Art
A portion of an eye which forms the exterior surface thereof is known as a cornea. For the eye to provide normal vision, the cornea has a spherical shape, an aspherical shape being the cause of a visual defect which is known as astigmatism. Accordingly, providing an indication of the asphericity of the cornea corresponds to providing an indication of the extent of the astigmatism of the eye.
It is desirable to provide the indication of the asphericity during an adjustment of sutures used to close an incision in the cornea during ophthalmic surgery. The incision closure is typically associated with a corneal transplant or a cataract removal. It should be appreciated that an operating microscope is almost always used by a surgeon to view the incision during the ophthalmic surgery.
Additionally, during a visit of a patient to the office of an ophthamologist it is often desirable to accurately measure the asphericity of an eye of the patient. The accurate measurement of the asphericity may be required for prescribing either opthalmic spectacle lenses or contact lenses.
The asphericity is measured by apparatus sold by American Optical Company and Bausch & Lomb, Inc. under marketing designations of Ophthalmometer and Keratometer, respectively. The apparatus is typically comprised of first and second illuminated symbols which are complementary to each other.
In a typical measurement of the asphericity, the ophthalmologist positions the first symbol at one of a plurality of selected locations with respect to the patient's eye and observes a reflection therefrom of an image of the first symbol. During the observation, the second symbol is positioned to cause a reflection from the patient's eye of an image of the second symbol superimposed upon the image of the first symbol. A notation is made of the relative positions of the symbols when the superimposed images are observed. Similarly, a superimposition and a notation is made when the first symbol is moved to each of the selected locations. The asphericity may be determined from the notations.
Because the apparatus is usually bulky, it may be an obstacle to the surgeon during the ophthalmic surgery. Additionally, the positioning of the symbols is time consuming and difficult.